1. Field of the Invention
The present invention relates to a novel imidazole compound, preferably an imidazole compound useful as a membrane-constituting lipid of a liposome, and a liposome containing the same.
2. Description of the Related Art
Recently, studies have been made for liposomes by which intraliposomal encapsulation of useful substances or release of useful substances in target cells can be controlled in response to an external pH. In particular, in a carrier which delivers a charged active ingredient such as nucleic acid, use of a pH-responsive lipid having pH-dependent charge characteristics as a membrane-constituting lipid of liposomes has been studied (JP2005-517739A).
To date, compounds containing an imidazole moiety (JP2005-526727A and U.S. Pat. No. 6,093,816A), and compounds containing a histidine moiety and a glutamic acid dialkyl ester moiety (WO2006/118327A) have been disclosed as pH-responsive lipids.